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+For the `--server` parameter, you can specify an ACME server directory URL,  and you can also give a short friendly name for known CAs.
+
+The supported short names are:
+
+|    Short Name      |       ACME server URL |
+|--------------------|    -------------------|
+| letsencrypt       |  https://acme-v02.api.letsencrypt.org/directory |
+| letsencrypt_test   | https://acme-staging-v02.api.letsencrypt.org/directory |
+| buypass  | https://api.buypass.com/acme/directory  | 
+| buypass_test |  https://api.test4.buypass.no/acme/directory |
+| zerossl | https://acme.zerossl.com/v2/DV90  |
+
+
+The short name will be treated as the same as the URL:
+
+The following usages have the same meaning:
+
+```
+acme.sh --issue ....   --server  zerossl
+
+-or-
+
+acme.sh --issue ....   --server  https://acme.zerossl.com/v2/DV90
+```
+
+
+